Historically, aircraft engine main fuel pumps primarily have been positive displacement type pumps, usually gear pumps which are relatively heavy devices
In aerospace applications, space and weight limitations are constant and perplexing problems. Consequently, centrifugal pump concepts have been pursued for main fuel pump applications because of benefits obtained in weight and reliability. However, two performance criteria which make it difficult to adapt centrifugal pumps to the engine main fuel pump application are dry lift and engine starting pressure requirements. Dry lift is the ability of a pump to draw fuel up a dry length of plumbing, thereby priming itself Engine starting pressure is the ability of the pump to generate enough pressure to start the engine while operating at the low speeds associated with engine start. One way to supplement a centrifugal pump's deficiencies at dry lift is to add a liquid ring pump in series with the main centrifugal stage. Liquid ring pumps have good lift performance capabilities. To supplement the centrifugal pump's inability to generate sufficient engine start pressures at low starting speeds, one could add a regenerative pump in series with the liquid ring and centrifugal main stages. The result is a three stage pump with three separate pumping elements, three different containment structures and three different sets of associated porting.
This invention contemplates an integral liquid ring and regenerative pump combining liquid ring and regenerative pumps into a single stage, thereby simplifying the design by reducing piece part count. This reduced piece part count has advantages in weight, envelope and reliability.